Extraction of Silica from Rice Husk Ash and Its Effect on the Properties of the Integral Membrane

Abstract

The large generation of agricultural residue could pose an environmental issue that lies through the disposal problem. Therefore, the incorporation of rice husk ash (RHA) into the membrane formulation could curb this problem besides adding value to the biomass. Rice husk ash is widely used as a filler for a polymer composite to enhance its mechanical properties due to the presence of silica. This research incorporated RHA into the membrane formulation. The silica in the RHA was extracted using an acid-leaching process and dried into silica powder. The silica powder was characterised by using an X-Ray diffractometer (XRD) and X-Ray fluorescence (XRF). A sol-gel method with hydrochloric acid as the catalyst was used in the fabrication of polysulfone/chitosan/polyvinyl alcohol membrane, and the extracted silica powder was incorporated in the formulations. The membranes were characterised in terms of functional groups using Fourier Transform Infrared Spectroscopy (FTIR), surface morphology using Scanning Electron Emission (SEM) analysis, and surface hydrophilicity using contact angle analysis. Finally, the performance of the membrane was analysed by pure water flux and antifouling. The XRD and XRF results showed that the extracted silica powder contained 77% of silica with the absence of impurities. The cross-linking reaction of membranes occurred as the Si–O–C bond was detected at 1,105cm−1 after the FTIR analysis, and a compact structure of the membrane was detected from the SEM analysis. The results from pure water flux portrayed that the membranes incorporated with silica (M1 and M2) had better integral stability compared to that from the pure polymer, which was observed from the consistent value of flux throughout the 1-hour filtration time and no swelling of the membranes after the performance testing. The results also showed that the extraction of silica from the RHA using a modified process was successfully conducted, and the silica powder was also compatible with the membrane solution as no separate layer was formed. Thus, the produced membranes have the potential to be used in the treatment of wastewater containing heavy metal ions.